1. Field of the Invention
This invention relates to a scanning illuminating device in a copying apparatus or the like in which irregularity of illumination due to the so-called cosine biquadratic rule of the projection lens is compensated for and the light sources are fixed which construction is suited for high-speed copying.
2. Description of the Prior Art
In most of the scanning illuminating systems of slit exposure type copying apparatus, a light source follows a scanning mirror. However, movement of the light source offers a problem as to durability including the cord or the like and is not suitable for high-speed copying. Re-issued U.S. Patent Re. No. 29017 discloses an illuminating system of a copying apparatus in which a light source (spot light source) is fixed. However, this uses a parabolic mirror to collimate the effective light beam and always brings about uniform illumination on the original surface and therefore, when the loss of quantity of light of the projection lens due to the cosine biquadratic rule is taken into consideration, the quantity of light becomes deficient at the marginal portion of the scanning direction and copying of uniform density over the entire picture plane cannot be accomplished.